This invention relates generally to a method for producing a hydrosulfite solution useful for brightening pulp.
Hydrosulfite can be generated by reacting aqueous sodium bisulfite solution with aqueous sodium borohydride solution. For example, U.S. Pat. No. 4,788,041 describes generation of hydrosulfite from a borohydride/hydroxide solution and a bisulfite solution. Sulfuric acid has been used to adjust the pH of the reaction mixture to an approximately neutral range. However, the sulfate salts generated from sulfuric acid do not have any utility in the papermaking process for which hydrosulfite usually is generated.
The problem addressed by this invention is to find a more effective method for brightening pulp using hydrosulfite.